1. Field of the Invention
The present invention relates to a safety vein syringe (intravenous syringe) in which the needle is retractable after injection.
2. Description of the Prior Art
Various types of disposable syringes are widely used nowadays. After being discarded, large amount of such syringes result in the problem of pollution of environment. The used syringes often impale medical personnel and infect the personnel with viruses or bacteria carried by the patients. Especially, in the case where the medical personnel are infected with AIDS virus, the personnel may die innocently. In order to solve these problems, various types of retractable syringes have been developed. For example, a spring is installed between the syringe barrel and the piston for pulling the needle back into the barrel after injection. However, due to the property of the liquid medicine, the material of the spring is strictly limited. Therefore, the structure of such syringe is complicated and the manufacturing cost is very high. Various types of safety vein syringes without springs have been also developed. In such syringes, a latch member is disposed at the bottom of the barrel, whereby when the plunger is pushed to the bottom of the barrel, the latch member latches the plunger with the needle. Therefore, when the plunger is pulled back, the needle is retracted into the barrel along with the plunger so as to avoid impalement of the medical personnel or other persons.
In order to avoid leakage of the liquid medicine and unexpected dropping of the needle from the barrel, the needle must be firmly assembled with the barrel. However, in the case that the needle is excessively firmly assembled with the barrel, it will be difficult to pull the needle back into the barrel. Therefore, it is troublesome to consider both situations.
With respect to the general syringe, many kinds of safety vein syringes have been developed in which the injection needle can be retracted into the syringe barrel after injection. However, with respect to the intravenous syringe, the central line of the injection needle is disaligned from the central line of the syringe barrel. Therefore, after injection and when it is desired to engage a needle pulling member disposed at the front end of the plunger with another needle pulling member disposed on the needle holder, it often takes place that the needle pulling member of the plunger cannot be aligned and engaged with the needle pulling member of the needle holder.
U.S. Pat. No. 5,242,402, Chen, shows a safety syringe with retractable self-biased needle adapted for intravenous injection. It provide a needle pulling members of the plunger and the needle holder respectively as an annular flange and an annular groove, in order to connect together in a manner that the annular flange inserts in the annular groove after injection. However, it is difficult to engage the annular flange and the annular groove with each other and the engaging strength therebetween is insufficient. Therefore, it often takes place that the needle holder is loosened from the plunger and cannot be pulled into the syringe barrel.
Therefore, as of the present time, all the conventional safety vein syringes have the above shortcomings and can be hardly used practically.